The present invention relates to low molecular weight polyesters which are prepared directly from hydroxypivaldehyde as a reactant.
It is known that hydroxypivaldehyde can be used as an intermediate in the preparation of drugs and polyesters. See, for example, Japanese Pat. No. 74 40443, which discloses a method for the preparation of hydroxypivaldehyde. However, due to the relative instability of hydroxypivaldehyde, prior art processes for the preparation of polyesters from hydroxypivaldehyde commonly include additional steps by which hydroxypivaldehyde is converted to a more stable ester prior to formation of the desired polyester. For example, U.S. Pat. No. 3,852,335 discloses the preparation of 2,2-dimethyl-1,3-propanediol-hydroxypivalic monoester which may then be used as a starting material for the manufacture of polyesters. U.S. Pat. No. 3,862,215 contains a similar disclosure.
The present invention provides a process by which low molecular weight polyesters are prepared directly from hydroxypivaldehyde as a reactant. The present process obviates the need for chemical conversion of the hydroxypivaldehyde prior to formation of the polyester, thereby eliminating one or more process steps. Consequently, there is a resulting savings in time and cost.
The product formed by the process of the present invention can be used in any application requiring a polyester diol or polyol. High solids coatings (75 weight percent or greater solids) prepared from the composition produced by the process of the present invention exhibit excellent gloss, solvent resistance, impact resistance, stain resistance, and humidity resistance.
The use of hydroxypivaldehyde as a reactant in the preparation of low molecular weight polyesters allows the introduction of unique neopentyl repeating units into the polyester. Hydroxypivaldehyde is readily available as the product of the reaction of isobutyraldehyde with formaldehyde.